agenis - 1 year ago 99

R Question

I want to plot the result of a PCA with the package factominer. When one plots a PCA it is good practice to resize the graph so that its H/L ratio is in proportion to the %variance explained by each axis.

So I tried first to resize the graph simply by stretching the window: it obviously fails and keep the points in the middle **instead of stretching them too.**

`library(FactoMineR)`

out <- PCA(mtcars)

Then I try to force the

`xlim`

`ylim`

`?plot.PCA`

`plot.PCA(out, choix="ind", xlim=c(-6,6), ylim=c(-4, 4))`

Same problem, the xlim limits are not respected...

Can someone explain this behaviour and knows how to fix it?

Answer Source

What you're seeing is the result of the call to `plot`

inside `plot.PCA`

:

```
plot(0, 0, main = titre, xlab = lab.x, ylab = lab.y,
xlim = xlim, ylim = ylim, col = "white", asp = 1, ...)
```

`plot`

is called with parameter `asp`

set to `1`

, which guarantees that the *y/x* ratio stays the same, so when you try to resize the window, the `xlim`

are recomputed.

In `plot.window`

you can find the "meaning" of `asp`

:

If asp is a finite positive value then the window is set up so that one data unit in the x direction is equal in length to asp * one data unit in the y direction.

You can try

```
plot(0, 0, main = "", xlab = "", ylab = "", xlim = c(-6, 6), ylim = c(-4, 4), col = "white", asp = 1)
```

and resizing the window, and then the same with

```
plot(0, 0, main = "", xlab = "", ylab = "", xlim = c(-6, 6), ylim = c(-4, 4), col = "white")
```

to see the difference.